1. Field of the Invention
The present invention is generally related to a passive air venting system used in a marine propulsion system and, more particularly, to a passive air vent using a hydrophobic or oleophobic membrane.
2. Description of the Prior Art
When marine engines are drained, or restarted after a period during which coolant has drained from the engine, it is necessary that the exchange of air and water be accomplished in a timely and efficient manner. When a marine propulsion system is in the process of evacuating its cooling water, it is important that steps be taken to avoid forming pockets of air in the cooling system which are subjected to decreasing pressure because of the sudden evacuation of water. In addition, when initially filling the cooling passages of a marine engine after water has been drained, it is important to evacuate the air from the system in an efficient manner to avoid xe2x80x9cvapor lockxe2x80x9d conditions that can inhibit the proper filling of the cooling passages with water.
U.S. Pat. No. 6,135,064, which issued to Logan et al on Oct. 24, 2000, discloses an engine drain system. The engine cooling system of a marine propulsion device is provided with a manifold that is located below the lowest point of the cooling system of an engine. The manifold is connected to the cooling system of the engine, a water pump, a circulation, the exhaust manifold of the engine, and a drain conduit through which all of the water can be drained from the engine.
U.S. Pat. No. 6,089,934, which issued to Biggs et al on Jul. 18, 2000, discloses an engine cooling system with a simplified drain and flushing procedure. The engine cooling system is provided with one or more flexible conduits attached to drain openings of the engine and its related components. First ends of the conduits are attached to the drain openings while the second ends are sealed by studs attached to a plate of a stationary bracket. A retainer is slidably associated with the flexible conduits and attached to a tether which is in turn attached to a handle. By manipulating the handle, the tether forces the retainer to slide along the flexible conduit and control the position of the second ends of the flexible conduits. This allows the system to be moved from a first position with the second ends of the conduits above the first ends of the conduits to a second position with the second ends of the conduits below the first ends and in the bilge of the boat. The system allows an operator to stand in a single location and move the drain system from the first to the second position and back again without having to reach down into the engine compartment to remove drain plugs. The system allows the cooling system to be easily drained or flushed.
U.S. patent application Ser. No. 09/887,823, which was filed Casey et al on Jun. 22, 2001, discloses a pump and drain apparatus for a marine propulsion system. An integral pump and drain apparatus is contained in a common housing structure to reduce the required space for these components in the vicinity proximate the engine of a marine propulsion system. The valve of the drain is remotely actuated by air pressure and therefore does not require the boat operator to manually remove plugs or manually actuate mechanical components to cause the engine to drain through a drain conduit that is formed as an integral part of the housing structure. U.S. patent application Ser. No. 09/891,121 which was filed by Jaeger on Jun. 25, 2001, discloses a siphon inhibiting device for a marine cooling system. The siphon inhibiting valve comprises first and second portions of a housing structure and a buoyant member disposed within the housing structure for movement along a first axis between an inlet port and an outlet port. The buoyant member is shaped to have a cylindrical portion and another portion which is shaped in the form of a frustum of a cone. Upward movement of the buoyant member causes an elastomeric seal on the buoyant member to come into contact with an internal lip formed in the housing structure, thereby creating a seal that prevents an upward flow of water in a direction from the outlet port to the inlet port. When cooling water is drained from the outlet port area, the buoyant member is forced downward into an open position by its own weight and the weight of the water on its inlet port side. This free movement of the buoyant member allows the water on the inlet port side to drain without manual intervention. When normal flow occurs, in a direction from an inlet port to the outlet port, the buoyant member is forced downward into an open position and water flows around the buoyant member from a water pump toward the cooling system of the engine. U.S. patent application Ser. No. 09/716,533 which was filed on Nov. 20, 2000, by Biggs et al discloses a marine engine cooling system with a check valve to facilitate draining. A marine engine cooling system is provided with a valve in which a ball moves freely within a cavity formed within the valve. Pressurized water, from a sea pump, causes the ball to block fluid flow through the cavity and forces pumped water to flow through a preferred conduit which may include a heat exchanger. When the sea pump is inoperative, the ball moves downward within the cavity to unblock the drain passage and allow water to drain from the head generating component of the marine engine. U.S. patent application Ser. No. 09/797,142 which was filed by Hughes et al on Mar. 1, 2001, discloses a marine engine cooling system with a simplified water drain and flushing mechanism. The draining system for a marine propulsion system is provided in which a manifold is located at a low portion of the cooling system to allow all of the water within the cooling system to drain through a common location or manifold. A rigid shaft is connected to a valve associated with the manifold and extending upwardly from the manifold to a location proximate the upper portion of the engine so that a marine vessel operator can easily reach the upper end of the shaft and manipulate the shaft to open the valve of the manifold. In this way, the valve can be opened to allow all of the water to drain from the engine without requiring the marine vessel operator to reach toward locations at the bottom portion of the engine.
U.S. Pat. No. 6,196,708, which issued to Rogers on Mar. 6, 2001, describes oleophobic laminated articles, assemblies of use, and methods. An article, such as a filter or film, has a treated laminate with an expanded PTFE membrane and a porous support scrim. The treated laminate is formed by contacting a laminate having an expanded PTFE membrane and a porous support scrim with an oleophobic treatment agent dissolved in an organic solvent. The oleophobic treatment agent is deposited onto the expanded PTFE membrane and porous support scrim as the organic solvent is removed. The oleophobic treatment agent is typically a fluoropolymer. The article can be used, for example, as a filter over a port in a housing of an electronics or other device.
U.S. Pat. No. 6,040,251, which issued to Caldwell on Mar. 21, 2000, describes garments of barrier webs. The invention includes a novel barrier web that has certain desirable physical characteristics such as water resistance, increased durability, improved barrier qualities and the like. The invention further comprises a barrier web comprising a web that has been treated with a curable shear thinned thixotropic polymer composition, the fabric being adapted to be substantially impermeable to liquids, permeable to gases and impermeable to microorganisms. The barrier webs of the present invention are either impermeable to all microorganisms or are impermeable to microorganisms of certain sizes. The present invention also includes fabrics that are capable of either selective binding certain microorganisms, particles or molecules depending upon what binding partners are incorporated into the polymer before application to the fabric.
U.S. Pat. No. 5,329,888, which issued to Luckett et al on Jul. 19, 1994, discloses a thermostat housing assembly for a marine engine. The assembly has a first inlet to receive sea water and an outlet that is connected to a circulating pump that circulates cooling water to the engine. A baffle is located in the housing and prevents direct flow between the sea water inlet and the outlet. The housing defines a pair of passages with a first of the passages providing communication between the sea water inlet and forms a first chamber which communicates with a pair of manifold outlets that are connected to the manifold. A second of the passages provides communication between the sea water inlet and the outlet of the circulation pump. The housing also includes a return inlet for returning water from the engine and the return inlet is connected to the second passages. A thermostat is mounted in an opening between the passages and when the thermostat is open a portion of the returning cooling water will be directed through the thermostat opening to the first passage and mixed with incoming sea water and then directed to the manifolds.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Various types of PTFE membranes and related oleophobic products are available in commercial quantities from W. L. Gore and Associates, Inc. and are sold under various trademarks, such as GORE-TEX fabrics, PreVent membrane vents, et al. W. L. Gore and Associates, Inc. also provides various types of automobile venting products such as those sold under the trade name OLEOGARD. These devices can be used to reduce the cost and weight of components by minimizing internal pressures which will result in reduced mechanical design requirements. The vents allow rapid exchange of air in response to pressure gradients while protecting against contamination by water, automobile fluids, and dust. The Pall Corporation provides various types of filter media components with properties that are useful in producing hydrophobic or oleophobic fabrics and materials.
When marine engine draining systems formerly required extensive manual intervention, the draining process was sufficiently slow to allow air to replace water as it drained from the engine. The highly improved draining systems, such as those described above, allow water to drain from the engine at a much faster rate and this quicker draining process can, under certain conditions, create pockets of air that are subjected to decreased pressure because of the evacuation of water from lower portions of the engine""s cooling system. As will be described in greater detail below, this rapid evacuation of water can possibly decrease the pressure within the cooling system sufficiently to draw water upwardly through the exhaust system of the engine and into the exhaust manifold. As is well known to those skilled in the art, water ingested into the region of the exhaust ports of the cylinders of the engine can lead to significantly deleterious results.
Also, when an engine is restarted after a period during which water has drained from its cooling passages, cooling water must be pumped from the body of water in which the marine propulsion system is operated and into the cooling passages of the engine to provide sufficient cooling capability. If air is not evacuated efficiently during this refilling operation, the condition referred to as xe2x80x9cvapor lockxe2x80x9d by those skilled in the art can occur and this improper filling of the cooling passages with water can lead to an overheating condition. It is therefore important that air be permitted to flow into and out of the engine cooling system at the appropriate times.
A marine propulsion system made in accordance with a preferred embodiment of the present invention comprises an engine having a cooling passage, a fluid conduit connected in fluid communication with the cooling passage, and a port formed at a preselected location of the fluid conduit. It further comprises a membrane covering the port, wherein the membrane is generally impermeable to liquid and generally permeable to gas.
The propulsion system further comprises a pump connected in fluid communication with the fluid conduit for drawing water from a body of water in which the marine propulsion system is operated and then pumping the water through the fluid conduit to the cooling passages of the engine. The fluid conduit can comprise a thermostat housing and the port can be formed in the thermostat housing. The thermostat housing is generally attached to a top portion of the engine and the port is located proximate a highest port of the fluid conduit in a particularly preferred embodiment of the present invention. The port is generally located proximate a point which is above the cooling passages of the engine in order to allow it perform its function more efficiently. The membrane covering the port is hydrophobic and, in certain embodiments, can also be oleophobic. The cooling passage of the engine comprises a cavity formed in a block of the engine to provide a path for cooling water to pass in thermal communication with heat producing components of the engine. The cooling passages within the engine are typically formed as cavities that are cast in the engine block when it is formed. These cavities are positioned so that water passing through them can efficiently remove heat from the heat producing portions of the engine.